In the design manufacture and operation of machine tools, there are many situations that arise which make it desirable to provide for an angular rotary adjustment between machine parts. The most common instance of this need has to do with the situation where the machine tool is provided with a rotary table which is capable of being accurately rotated on occasion to present another portion of a workpiece to the tool or to bring another workpiece into operative relationship to the tool. In order to perform accurate machining, the workpiece must be located accurately in the conventional six modes of motion and, while some such rotary tables produce accuracy adequately in one or two modes, it is difficult economically to design one that is accurate in all six modes.
It has been suggested in the past that the elements of a table can be accurately located relative to one another by use of a toothed coupling known as the "curvic" coupling. Entering engagement of the mating teeth of the curvic coupling is such that location of the elements relative to one another can be produced in the six modes very accurately. However, the toothed coupling of this type suffers from the disability that the accuracy of location depends upon the mating of accurately-formed surfaces having a limited area of contact. This means that the coupling is unable to resist large forces in certain modes of motion. For instance, in the case of a worktable which may carry a heavy weight of workpieces, the large axial forces between the two parts of the coupling would lead to inaccuracy and extreme wear of the locating surfaces. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a machine tool having angularly adjustable elements which are capable of considerable accuracy, while at the same time being able to absorb large forces.
Another object of this invention is the provision of a machine tool having a heavy duty rotary table in which the table angular position can be determined very accurately.
A further object of the present invention is the provision of a machine tool having angular location means which is purely mechanical, but which, nevertheless, is capable of great accuracy.
It is another object of the instant invention to provide a machine tool having an angularly-adjustable worktable which is simple in construction and which is capable of a long life of useful service with a minimum of maintenance.
A still further object of the invention is the provision of a machine tool having a worktable which can be rotated to a new angular position, which new position is first inaccurately determined by a powerful means and finally accurately determined by a less powerful means.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.